The invention relates to manufacturing magnetic circuits, in particular the stator magnetic circuits of electrical rotary machines.
It is known to make the magnetic circuits of electrical rotary machines by stacking magnetic laminations that are provided with slots.
French patent application FR-A-2 109 301 discloses a manufacturing method in which a strip of sectors that are connected to one another by narrow portions serving as respective hinges are wound on a mandrel. Once winding has been completed, the narrow portions lie inside the outside diameter of the stator and do not project outwards.
When the narrow portions are deformed during the winding operation, they tend to take up a small amount of curvature outside the plane of the sector, which tends to interfere with bringing the stacked sectors into face-against-face contact.
Japanese patent application JP 11 234 973A describes a yoke made up of interconnected sectors.
Japanese patent application JP 09 308 143A describes sectors each comprising merely a tooth, and interconnected by bridges of material.
The invention seeks to facilitate and improve the manufacture of magnetic circuits for electrical machines, in particular rotary machines of large dimensions in which the bore diameter of the stator is greater than or equal to 300 millimeters (mm).
The invention achieves this by a novel strip of lamination sectors for making the magnetic circuit of an electrical machine, in which the sectors are interconnected by links, the strips being designed to be wound on a mandrel to form a stack of layers of sectors, wherein said links are outside the sectors, each sector preferably having at least one slot for passing electrical conductors.
The invention improves contact between the sectors of the stack since the link portions extend outside the plane of the sectors and are therefore situated outside the outside diameter of the stack.
In a preferred implementation, said links are constituted by bridges of deformable material or bridges obtained by being cut out together with the sectors.
In a variant, the links are hinged links provided by staples.
The shape given to the above-mentioned bridges of material is selected to enable them to deform while the strip of sectors is being wound on the mandrel.
Each of the bridges can have a portion presenting two parallel edges.
In a variant, each of the bridges of material can present two narrowings on either side of a middle portion, said narrowings constituting preferred zones for deformation.
In another variant, each of the bridges of material can present concentric edges.
Advantageously, each bridge of material has an edge situated in line with the lateral edge or docking flank of a sector to which it is connected.
Advantageously, the sectors have complementary profiles on their docking flanks so as to ensure proper radial positioning of the sectors during winding.
These complementary profiles can include a tooth on one of the flanks and a notch on the other flank, preferably a notch of complementary shape, the tooth preferably having edges that converge and the notch having edges that diverge.
The invention also provides a method of manufacturing the magnetic circuit of an electrical machine, the method comprising the steps consisting in:
making a strip of lamination sectors interconnected by deformable and/or hinged links, two consecutive sectors within said strip presenting adjacent lateral edges forming an angle between each other; and
winding the strip of sectors on a mandrel so as to move said edges towards each other and thus make up a stack of layers of sectors, each sector being cut out in such a manner that its angular extent is different from an integer submultiple of a complete turn.
This avoids superposing the links which are thicker than the sectors and would otherwise prevent the layers from touching completely.
Preferably, the length of the sectors is selected in such a manner as to limit the frequency with which junctions between sectors are superposed.
This avoids superposing breaks in the magnetic circuit, thereby limiting electrical losses and providing the stack with better mechanical cohesion.
The invention makes it easy to make a magnetic circuit for an electrical machine continuously by winding the strip of sectors on a mandrel whose outside diameter is greater than or equal to 300 mm, for example.
Preferably, said mandrel is rotated.
Also preferably, the angular width xcfx89 of a sector is equal to 360xc2x0. (1/kxc2x1j/nd), where nd is the total number of slots per complete turn, k is a non-zero integer submultiple of nd, and j is an integer.
Advantageously, nd is selected from the following values: 48; 60; 72; 84; 96, j lies in the range 1 to 3, and k is greater than or equal to 3, preferably equal to 6.
The invention also provides a magnetic circuit for an electrical machine, the circuit comprising a stack of layers of sectors formed by helically winding a strip of sectors that are interconnected by deformable and/or hinged links situated peripherally, outside the stacked sectors.
In a particular embodiment, the bars are fixed to the periphery of the stack, being engaged in or between the deformable and/or hinged links interconnecting the sectors.
Advantageously, said deformable and/or hinged links serve a guides for fixing the bars, which bars serve to keep the layers of sectors in contact and advantageously constitute cooling channels with the case of the machine.
The fact that the links between sectors project outside the stack increases the heat exchange area in the cooling air channel around the magnetic circuit.
In addition, the discontinuous distribution of links in the air channel has the effect of making the air flow more turbulent and of increasing the heat exchange coefficient.
The invention also provides an electrical machine including a magnetic circuit, in particular a stator, as defined above.